Heat oil in a medium frying pan over high heat. Add mushrooms and cook, tossing frequently,
for 6 minutes or until mushrooms are tender. Stir in balsamic vinegar and cook
for 1 minute. Combine 1 tablespoon stock, cornflour and brown sugar in a small
bowl. Stir this cornflour mixture and remaining stock into mushrooms. Bring to
the boil, stirring often. Reduce heat to medium and cook, stirring
occasionally, for 5 minutes or until sauce thickens slightly. Stir in thyme and
season with salt and pepper. Serve mushroom sauce with barbecued steaks or toss
mushroom sauce in pasta and serve with grated parmesan cheese.